Device for applying magnetic field to a filter for reducing metallic contaminants

ABSTRACT

A filter is used for removing metallic contaminants in a solvent used in microcircuit fabrication. The filter includes a filter housing including a filter membrane for filtering solvent including metallic contaminants, and a magnet arranged about the filter housing and configured to generate a magnetic field to attract the metallic contaminants prior to the metallic contaminants entering the filter membrane. The magnet is arranged such that the magnetic field of the magnet is greater in a periphery of the filter housing compared to a central portion of the filter housing.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority of U.S. Provisional Patent ApplicationNo. 62/753,915 filed on Oct. 31, 2018, the entire contents of which areincorporated herein by reference.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experiencedrapid, growth. Technological advances in IC materials and design haveproduced generations of ICs where each generation has smaller and morecomplex circuits than the previous generation. However, these advanceshave increased the complexity of processing and manufacturing ICs and,for these advances to be realized, similar developments in IC processingand manufacturing are needed. In the course of integrated circuitevolution, functional density (i.e., the number of interconnecteddevices per chip area) has generally increased while geometry size(i.e., the smallest component (or line) that can be created using afabrication process) has decreased.

As pattern sizes of semiconductor devices become smaller andsemiconductor devices having new structures are developed,contaminant-free liquids have been used for fabricating integratedcircuits. Point-of-use (POU) filters are designed to remove contaminantsfrom the liquids used in integrated circuit manufacture. For example,during photolithographic processes, the photoresist is filtered tominimize presence of metal contaminants/impurities and minimize defectsin photoresist patterns.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposesonly. In fact, the dimensions of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIG. 1 is a schematic view of an apparatus for applying a solvent to asemiconductor wafer, according to embodiments of the disclosure.

FIG. 2A schematically illustrates an elevation view of a filter havingmagnets arranged about the filter, according to embodiments of thedisclosure.

FIG. 2B illustrates a cross-sectional view of the filter in FIG. 2Ataken along line 2B-2B in FIG. 2A.

FIG. 2C illustrates a magnet in FIG. 2A, according to embodiments of thedisclosure.

FIG. 2D illustrates a partial cross-sectional view of the filter in FIG.2A, according to embodiments of the disclosure.

FIG. 2E schematically illustrates a fluid flow inside the filter housingof the filter in FIGS. 2A and 2B having magnets attached thereto,according to embodiments of the disclosure.

FIG. 3 is a graph illustrating reduction in metallic impurities usingthe arrangement in FIGS. 2A and 2B.

FIG. 4A schematically illustrates an elevation view of the filter inFIG. 2A including a plurality of magnetic arc segments, according toembodiments of the disclosure.

FIG. 4B is a cross-sectional view of the filter in FIG. 4A taken alongthe line 4B-4B in FIG. 4A, according to embodiments of the disclosure.

FIG. 4C illustrates a magnetic arc segment in FIG. 4A, according toembodiments of the disclosure.

FIG. 4D illustrates another magnetic arc segment in FIG. 4A, accordingto embodiments of the disclosure.

FIG. 4E schematically illustrates a fluid flow in the filter in FIG. 4Ahaving magnets attached thereto, according to embodiments of thedisclosure.

FIG. 5A is a graph illustrating sample results of an experiment to studythe reduction in metallic impurities using the magnetic arrangement inFIG. 4A, according to embodiments of the disclosure.

FIG. 5B is a graph illustrating sample results of another experiment tostudy the reduction in metallic impurities using the magneticarrangement in FIG. 4A, according to embodiments of the disclosure.

FIG. 6 is a flow chart illustrating a method of developing an exposedphotoresist according to an embodiment of the present disclosure.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof the disclosure. Specific embodiments or examples of components andarrangements are described below to simplify the present disclosure.These are, of course, merely examples and are not intended to belimiting. For example, dimensions of elements are not limited to thedisclosed range or values, but may depend upon process conditions and/ordesired properties of the device. Moreover, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed interposing the first and second features, suchthat the first and second features may not be in direct contact. Variousfeatures may be arbitrarily drawn in different scales for simplicity andclarity.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The device may be otherwise oriented (rotated 90 degrees orat other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly. In addition, the term“made of” may mean either “comprising” or “consisting of.”

Contaminant-free fluids (e.g., photoresist, developer, etchant, etc.)are used in the fabrication of integrated circuits. Point-of-use filtersare designed as the last opportunity to remove contaminants from thefluids used in integrated circuit manufacture. A point-of-use filterprocesses fluid which is to be utilized immediately in a localizedmanufacturing step. The manufacture of integrated circuits involvesmultiple steps in which silicon wafers are repeatedly exposed toprocesses such as lithography, etching, doping, and deposition ofmetals. Throughout all of these steps, the semiconductive nature of thesilicon and its surface must be maintained and/or specificallycontrolled. Contamination can alter the semiconductive nature of thesilicon or disturb the intended circuit design, thereby reducing theyield of integrated circuits. Particles as small as 0.1 micrometer may,therefore, lead to failure of a semiconductor element. A particle canprevent the completion of a line or a particle can bridge across twolines. Contamination can be either direct on the silicon surface or itmay be a contamination of a masking surface, changing the circuit designwhich is printed. Point-of-use filters must, therefore, removemicroparticulates that would cause defects.

In addition, a point-of-use filter should not add contaminants, such aslow levels of ionic and total organic carbon (TOC) extractables.Extractables are substances which may be potentially released from afilter element and contaminate its effluent. If such contaminants aredeposited on silicon wafers, they may cause defects, resulting in ayield loss during the fabrication of integrated circuits. As a result,industry practice is to test the resistivity of the effluent at thepoint-of-use filters. Only after the effluent has reached the level ofpurity of the influent can the effluent be used for fabricatingintegrated circuits.

Embodiments of the disclosure are directed to a device for applying amagnetic field around a filter for filtering solvents used inphotolithography, wet etching, wet cleaning or similar operationsperformed on a semiconductor wafer. Some embodiments are directed toreducing metal defects in a photoresist development process by applyinga magnetic field around a filter (e.g., a point-of-use (POU) filter)used to filter a solvent used in the photoresist development process. Insome embodiments, the solvent is tetramethylammonium hydroxide (TMAH)used in developing exposed photoresist or etching operations. Thefiltering minimizes metallic contaminants (ions or charged particles)such as iron (Fe), aluminum (Al), and the like. The metalliccontaminants in the solvents may introduce scum defects, which areundesirable presence of the metallic particulate matter around patternson the wafer. By filtering the metallic contaminants, the scum defectsmay be reduced. Although embodiments are discussed with reference toreducing metal defects in a positive tone development (PTD) process, theprinciples disclosed herein are equally applicable to filteringsolutions used in other processes such as, but not limited to, negativetone development (NTD) process.

FIG. 1 is a schematic view of an apparatus 100 for depositing a solventon a semiconductor wafer, according to embodiments of the disclosure.One of ordinary skill in the art would, understand that one or moreadditional features are utilized with the apparatus 100 shown in FIG. 1.Additionally, although the apparatus 100 is discussed as being used todeposit a solvent on a semiconductor wafer, embodiments are not limitedthereto. In other embodiments, the apparatus 100 is used to deposit thesolvent or a fluid on any desired substrate, without departing from thescope of the disclosure.

The apparatus 100 includes a housing or an enclosure 101 in which asubstrate holder 103 is disposed. The substrate holder 103 is configuredto hold or secure a semiconductor wafer 110 and to rotate thesemiconductor wafer 110 at various speeds. The apparatus 100 includesseveral fluid nozzles, including a first fluid nozzle 121 configured todispense the solvent to be deposited on the semiconductor wafer 110, asecond fluid nozzle 123 configured to dispense a cleaning solution toclean the semiconductor wafer 110, and a third fluid nozzle 125configured to dispense de-ionized water onto the semiconductor wafer110. The nozzles 121, 123, and 125 are movable in transverse directionsand in the vertical direction in some embodiments. Although theapparatus 100 is discussed as including three nozzles, the number ofnozzles is not limited thereto and can be increased or decreased.Further, a UV light source or a heater 130 is disposed inside or outsidethe housing 101.

The first fluid nozzle 121 is fluidly connected to a solvent source 115holding the solvent, and the second fluid nozzle 123 is fluidlyconnected to a cleaning solution source 150 holding the cleaningsolution. In other embodiments, the source 150 stores a photo resisttank or bottle. Further, the third fluid nozzle 125 is fluidly connectedto a de-ionized water source, which may be a facility de-ionized watersource.

In some embodiments, a filter (e.g., point-of-use filter) 200 is fluidlyconnected to the solvent source 115 to filter the solvent provided tothe first fluid nozzle 121. In other embodiments, a filter 260 isfluidly connected to the cleaning solution source 150 to filter thecleaning solution provided to the second fluid nozzle 123. The filter260 may be similar to the filter 200 in some respects.

At least some of the operations of the apparatus 100 are controlled byone or more controllers 180 connected to or including one or more memorydevices 190. The controller 180 is a computer system including one ormore processors and the memory devices 190 store computer readableprogram code, in some embodiments. The controller 180 can be ageneral-purpose microprocessor, a microcontroller, a digital signalprocessor (DSP), an application specific integrated circuit (ASIC), afield programmable gate array (FPGA), a programmable logic device (PLD),a controller, a state machine, gated logic, discrete hardwarecomponents, or any other suitable entity that can perform calculationsor other manipulations of information. The one or more memory devices190 can be a random access memory (RAM), a flash memory, a read onlymemory (ROM), a programmable read-only memory (PROM), an erasable PROM(EPROM), registers, a hard disk, a removable disk, a CD-ROM, a DVD, orany other suitable storage device, for storing information and computerreadable program code to be executed by controller 180.

When the program code is executed by the controller 180, the controller180 controls the operations of, for example, the substrate holder 103,the nozzles 121, 123 and 125, fluid flows of the solutions flowing,therethrough, and a heater/UV light source 130.

According to embodiments, the magnetic field is applied using aring-shaped (or annular) magnet arranged in an N-S-N-S sequence aboutthe filters 200 and/or 260. The filters 200 and/or 260 have acylindrical filter housing in some embodiments and the ring-shape, maythus, increase the contact area of the magnet with the filter. However,the shape and type of the magnets are not limited in this regard. Insome embodiments, neodymium magnets are used. In other embodiments,other types of magnets having a desired shape (e.g., bar shape) thatprovide the desired results (e.g., adequate reduction in contaminants asdesired for the fabrication process) may be used.

FIG. 2A schematically illustrates an elevation view of the filter 200(and/or 260) having magnets 204-1, 204-2, 204-3, and 204-4 arrangedabout the filter 200, according to some embodiments. FIG. 2B illustratesa cross-sectional view of the filter 200 taken along line 2B-2B in FIG.2A. In some embodiments, the filter 200 is used as a point-of-use filterfor filtering metallic contaminants present in solvents (e.g., TMAH)used in the development operation in wafer fabrication. However,embodiments are not limited in this regard. Embodiments disclosed hereinare equally applicable to other wafer fabrication operations that usefiltered solvents, without departing from the scope of the disclosure.Further, embodiments discussed herein with reference to filter 200 areequally applicable to filter 260 in FIG. 1, without departing from thescope of the disclosure.

In the arrangement illustrated in FIGS. 2A and 2B, four magnets 204-1,204-2, 204-3, and 204-4 (collectively, magnets 204) are arranged aboutthe filter 200. The magnets 204 may be neodymium magnets. In otherembodiments, the magnets 204 are electromagnets. However, magnets 204are not limited to neodymium magnets or electromagnets or a particularmagnet. Any magnet can be used according to application and userpreferences. The magnets 204 are attached to an external surface 215 ofa filter housing 206 and are secured using a restraining device. In anembodiment, and as illustrated, the restraining device is a band 270.The ends of the band 270 are coupled to each other using by fasteners(nuts and bolts, screws, pins, rivets, anchors, seams, crimps,snap-fits, shrink-fits, etc.). Further, the band 270 is adjustable suchthat the band 270 can be used to secure the magnets 204 to filterhousings of different sizes (e.g., diameters). Although, only one band270 is illustrated, it will be understood that more than one band 270can be used to secure the magnets 204.

FIG. 2C illustrates magnet 204-1, according to embodiments of thedisclosure. Magnets 204-2, 204-3, and 204-4 in FIGS. 2A and 2B aresimilar to magnet 204-1. As illustrated, magnet 204-1 is a bar or blockmagnet having an axis of magnetization in the thickness (T) dimensionand perpendicular to the length (L) and width (W) dimensions of themagnet 204-1. Referring to FIGS. 2A and 2B, the magnets 204 are attachedto the external surface 215 of the filter housing 206 in the lengthwisedirection.

FIG. 2D illustrates a partial cross-sectional view of the filter 200,according to embodiments of the disclosure. It should be noted that thefilter 200, as discussed herein, is merely an example of a variety ofdifferent filters that can used to filter the solvent (or other fluids)to minimize the content of the metallic contaminants therein. It will beunderstood that the structure of the filter 200 is not limiting in anyregard and the magnets 204 can used with other types of filters forfiltering metallic contaminants, such as ions, according to embodimentsdiscussed herein and without departing from the scope of the disclosure.For the sake of clarity of illustration, the magnets 204 and the band270 are omitted in FIG. 2D.

As illustrated, the filler housing 206 includes, or otherwise defines,an inlet 201 and an outlet 203 of the filter 200.

The inlet 201 and the outlet 203 are located on an upper surface of thefilter housing 206 in some embodiments. However, the inlet 201 and theoutlet 203 can be located at other locations on the filter housing 206in other embodiments. The filter housing 206 is a generally cylindricalstructure made of high-density polyethylene (HDPE), or similar material.The filter housing 206 defines, or otherwise includes, an inner volume221 into which the solvent to be filtered is introduced using the inlet201 and from which filtered solvent is removed using the outlet 203. Thefilter housing 206 also encloses in the inner volume 221 a filter cage207 including a filter membrane 209. The filter membrane 209 is a hollowcylindrical structure that is installed within the filter cage 207. Thefilter cage 207 provides support to the filter membrane 209 andmaintains the shape and form of the filter membrane 209. In someembodiments, and as illustrated, the filter cage 207 is centrallylocated in the filter housing 206. However, in other embodiments, thefilter cage 207 is radially offset from the center of the filter housing206.

As illustrated, the inlet 201 is located along a periphery or an outeredge of the upper surface of the filter housing 206. The outlet 203 isin fluid communication with the filter cage 207 such that the solvent(or other fluids) after filtering by the filter membrane 209 exits thefilter 200 via the outlet 203. Solvent (or other fluid) to be filteredis introduced into the filter 200 via the inlet 201 and passes through apassageway 211 that is fluidly connected to the inlet 201. Thepassageway 211 isolates upper portions of the filter cage 207 and thefilter membrane 209 from the solvent introduced in the filter housing206 and directs the solvent to bottom portions of the filter housing206. The passageway 211 isolates the solvent from the filter cage 207and the filter membrane 209 part way through the filter housing 206, andthereby prevents the solvent from contacting the filter cage 207 and thefilter membrane 209 directly upon being introduced into the filterhousing 206. The filter housing 206 also includes (or otherwise defines)a vent 205 that is located on the upper surface of the filter housing206. The vent 205 functions to purge contaminated solvent prior to thesolvent passing through the filter membrane 209.

Referring to FIGS. 2A, 2B, 2C, and 2D, the magnets 204 are attachedlengthwise to the external surface 215 of the filter housing 206. In anembodiment, and as illustrated, circumferentially adjacent magnets 204have opposite polarity poles contacting the filter housing 206.Additionally, diametrically opposite magnets 204 have the same polaritypoles contacting the filter housing 206.

Such an arrangement of magnets 204 results in a reduced net magneticfield in the central region of the filter housing 206 including thefilter membrane 209 and the metallic contaminants are attracted to theperiphery of the filter housing 206, as discussed below. Statedotherwise, the magnetic field is greater in the peripheral portion ofthe filter housing 206 compared to the magnetic field in the centralportion of the filter housing 206.

The number of magnets 204 is not limited in any regard and the number ofmagnets 204 can be increased or decreased as needed by the applicationand design and without departing from the scope of the disclosure. Insome embodiments, the number of magnets is six or eight. The shape ofthe filter housing 206 is also not limited in any regard. The housingcan have any desired shape and any number of magnets 204 can be arrangedon the filter housing 206 in a desired arrangement provided the magneticfield in the peripheral portion of the filter housing 206 is greaterthan the magnetic field in the central portion of the filter housing206.

FIG. 2E schematically illustrates a fluid flow inside the filter housing206 of the filter 200 having magnets 204 attached thereto, according toembodiments of the disclosure. For the sake of clarity of illustration,the band 270 is omitted in FIG. 2E. As illustrated, solvent (or anyfluid) from which metallic contaminants are to be filtered is introducedinto the filter housing 206 via the inlet 201. The solvent flows throughthe passageway 211 into portions of the filter housing 206 outside thefilter membrane 209. Specifically, the solvent occupies the portions ofthe filter housing 206 outside the filter membrane 209 prior to flowingthrough the filter membrane 209. The arrangement of the magnets 204-1and 204-3 (with the S poles facing each other) causes magnetic fields231 of the magnets 204-1 and 204-3 to repel each other. Likewise, thearrangement of the magnets 204-2 and 204-4 (with the N poles facing eachother) causes magnetic fields of the magnets 204-2 and 204-4 to repeleach other. As a result, the magnetic field 231 due to the magnets 204is reduced (e.g., negligible) in the central portion of the filterhousing 206 and the metallic contaminants 251 (iron (Fe) particles oraluminum (Al) particles as illustrated) are attracted to the innersurface 213 of the filter housing 206 due to the magnetic field from themagnets 204 and are thus trapped. The metallic contaminants are trappedbefore the entering the filter membrane 209. As a result, the life ofthe filter membrane 209 is increased and the filter membrane 209 can bereplaced at frequently. Because of a pressure differential between theinlet 201 and the outlet 203, the solvent passes through the filtermembrane 209 where other contaminants (e.g., non-metallic contaminants)not removed due to the magnets 204 are filtered. The solvent then exitsthe filter 200 via the outlet 203. In some embodiments, the exitingsolvent is recirculated through the filter 200. Recirculating thesolvent increases the number of metallic contaminants that are filteredfrom the solvent. In some embodiments, the pressure differential isadjusted to reduce the flow of the solvent through the filter 200. Byreducing the flow, the solvent is exposed to the magnetic field for arelatively longer time period and an increased number of metalliccontaminants are filtered from the solvent. By controlling the flow ofthe solvent through the filter 200 and/or by recirculating the solventthrough the filter 200, the amount of metallic contaminants filteredfrom the solvent can be increased.

FIG. 3 is a graph 300 illustrating the reduction in metallic impuritiesusing the magnet arrangement in FIGS. 2A-2E. As illustrated, when usingthe magnetic arrangement of the magnets 204, a reduction of about 33% inthe number of metallic contaminants is observed from a baseline (BSL)measurement performed in the absence of the magnets 204.

FIG. 4A schematically illustrates an elevation view of the filter 200having magnets 404-1, 404-2, 404-3, and 404-4 arranged about the filter200, according to embodiments of the disclosure. FIG. 4B is across-sectional view of the filter 200 taken along the line 4B-4B inFIG. 4A. For the sake of explanation, embodiments are discussed withreference to the filter 200 of FIGS. 2A and 2B. However, it will beunderstood that embodiments are not limited in this regard. Other typesof filters can also be used with the magnets 404-1, 404-2, 404-3, and404-4, without departing from the scope of the disclosure.

Referring to FIGS. 4A and 4B, the magnets 404-1, 404-2, 404-3, and 404-4(collectively, magnets 404) are each shaped as arc segments that areattached to the external surface 215 of the filter housing 206. Themagnets 404 are arranged such that adjacent magnets have oppositepolarity poles contacting the filter housing 206, and diametricallyopposite magnets have same polarity poles contacting the filter housing206. Each magnet 404-1, 404-2, 404-3, and 404-4 is sized and shaped (orotherwise configured) such that an entire inner radial surface 415 or417 (FIGS. 4C and 4D) of a magnet contacts the external surface 215. Asillustrated, the magnets 404-1, 404-2, 404-3, and 404-4 are arrangedend-to-end (e.g., each magnet 404 contacts a circumferentially adjacentmagnet) to form a ring type magnet and thereby overlap the entireinternal volume 221 of the filter housing 206. In some embodiments, andas illustrated, a restraining device 270, e.g., a band, is used tosecure the magnets 404 on the external surface 215. As mentioned above,the band 270 is adjustable such that the band 270 can be used to securethe magnets 404 of different sizes (e.g., arc lengths) for filterhousings of different sizes (e.g., diameters). Although, only one band270 is illustrated, it will be understood that, more than one band 270can be used to secure the magnets 404. As illustrated, diametricallyopposite magnets have poles of the same polarity facing each other.Thus, the magnetic fields 231 (FIG. 4E) of the magnets repel each other.As a result, a reduced magnetic field is produced in the central portionof the filter housing 206 including the filter membrane 209 and themetallic contaminants are attracted to the inner surface 213 of thefilter housing 206. Stated otherwise, the magnetic field due to themagnets 404 is greater in the peripheral portion of the filter housing206 compared to the magnetic field in the central portion of the filterhousing 206.

The magnets 404 may be a neodymium magnet. In other embodiments, themagnets 404 are electromagnets. However, the magnets 404 are not limitedto a neodymium magnet, electromagnet, or any particular magnet, and anymagnet can be used according to application and user preferences.

FIG. 4C illustrates the magnet 404-1 (or 404-3), according toembodiments of the disclosure. FIG. 4D illustrates the magnet 404-2 (or404-4), according to embodiments of the disclosure. As illustrated inFIG. 4C, a radially inner portion of each magnet 404-1 and 404-3includes the north (N) pole and a radially outer portion of each magnet404-1 and 404-3 includes the south (S) pole. The arrangement of thepoles is opposite in magnets 404-2 and 404-4. As illustrated in FIG. 4D,a radially inner portion of each magnet 404-2 and 404-4 includes thesouth (S) pole and a radially outer portion of each magnet 404-2 and404-4 includes the north (N) pole. A thickness (T) of each magnet 404-1,404-2, 404-3, and 404-4 is such that the magnets cover the entireexternal surface 215 of the filter housing 206 when attached thereto.

Although filter 200 is illustrated as including four magnets 404-1,404-2, 404-3, and 404-4, embodiments are not limited thereto. In someother embodiments, the filter 200 includes more than four magnets. Instill other embodiments, a magnet formed by a single unitary ring-shapedpiece of material that is magnetized such that circumferentiallyadjacent arc portions have opposite polarity poles contacting the filterhousing 206 can be used. In such an embodiment, the magnet has anopening that is shaped and sized (or otherwise configured) to receivethe filter housing 206.

In some embodiments, the magnets 404-1, 404-2, 404-3, and 404-4 have athickness (T) smaller than the height of the filter housing 206 suchthat the magnets 404-1, 404-2, 404-3, and 404-4 do not cover the entireexternal surface 215 of the filter housing 206. In such embodiments, theuncovered portion of the filter housing 206 is covered by other magnetssimilar to magnets 404-1, 404-2, 404-3, and 404-4.

The magnets 404-1, 404-2, 404-3, and 404-4 increase the contact areawith the filter housing 206 and metallic contaminants in the solvent areattracted over the increased surface area of the inner surface 213.

FIG. 4E schematically illustrates a fluid flow in the filter 200 havingthe magnets 404-1, 404-2, 404-3, and 404-4 attached thereto, accordingto embodiments of the disclosure. For the sake of clarity ofillustration, the band 270 is omitted in FIG. 4E. The fluid flow and theseparation of the metallic contaminants when using the magnets 404 issimilar to the fluid flow and the separation of the metalliccontaminants when using the magnets 204 in FIG. 2E. Briefly, solvent (orany fluid) from which metallic contaminants are to be filtered isintroduced into the filter housing 206 via the inlet 201. The solventflows through the passageway 211 into portions of the filter housing 206outside the filter membrane 209. As illustrated, metallic contaminants251, such as iron (Fe) or aluminum (Al) particles, are attracted to theinner surface 213 of the filter housing 206 due to the magnetic fieldfrom the magnets 404 and are trapped. The metallic contaminants aretrapped before the entering the filter membrane 209. As a result, insome embodiments, the life of the filter membrane 209 is increased andthe filter membrane 209 is replaced less frequently. The solvent passesthrough the filter membrane 209 and exits the filter 200 via the outlet203. In some embodiments, the exiting solvent is recirculated throughthe filter 200. Recirculating the solvent increases the number ofmetallic contaminants that are filtered from the solvent. In someembodiments, the pressure differential between the inlet 201 and theoutlet 203 is adjusted to reduce the flow of the solvent through thefilter 200. By reducing the flow, the solvent is exposed to the magneticfield of the magnets 404 for a relatively longer time period and anincreased number of metallic contaminants are filtered from the solvent.By controlling the flow of the solvent through the filter 200 and/or byrecirculating the solvent through the filter 200, the amount of metalliccontaminants filtered from the solvent can be increased.

FIG. 5A is a graph 502 illustrating results of an experiment to studythe reduction in metallic contaminants using the magnetic arrangement inFIGS. 4A and 4B, according to embodiments of the disclosure. Inconducting the experiment, the pixel size of the recipe in the particlemeasurement tool was set to 15 nm. A solution (e.g., a resist developingsolution) that was filtered for multiple continuous days using thefilter 200 including the magnets 404 is dispensed on an uncoated (bare)wafer. The wafer was then scanned using the particle measurement tool toobtain particle count. As indicated in the graph 502, the metalliccontaminant count decreased as the number of days the solution wasfiltered increased. For instance, as indicated, the metallic contaminantcount was 15 in day 4 and day 6, on day 13 the metallic contaminantcount was 10, and the metallic contaminant count was 7 on day 19. Theaverage daily metallic contaminant count was determined to be 12. Areduction of about 45% was observed on average in the metalliccontaminant count from a baseline (BSL) measurement performed afterfiltering in the absence of the magnet 404.

FIG. 5B is a graph 504 illustrating results of another experiment tostudy the reduction in metallic impurities using the magneticarrangement in FIGS. 4A and 4B, according to embodiments of thedisclosure. In conducting the experiment, a test wafer was coated withmiddle layer (ML) and photoresist (PR) and was exposed by the scanner.Then, a solution (e.g., a resist developer) that was filtered formultiple continuous days using the filter 200 including magnets 404 isdispensed on the exposed wafer to remove the photoresist. An etch backprocess was performed to etch the middle layer. The wafer was thenscanned using the particle measurement tool to obtain particle count. Asindicated in the graph 504, the metallic contaminant count generallydecreases as the number of days the solution was filtered increased. Forinstance, the metallic contaminant count was 6 on day 4 and was 9 on day6. On day 13, the metallic contaminant count was 4, the metalliccontaminant count was 5 on day 15, and was 8 on day 26. An overallreduction of about 45% was observed on average in the number of metalliccontaminant count from a baseline (BSL) measurement performed in theabsence of the magnet 404.

According to embodiments, the filter 200 in FIGS. 2A-2E and FIGS. 4A and4B is used to filter a developer solution used in photolithographicoperations for semiconductor fabrication. Typically, in semiconductorfabrication, a photoresist layer is applied to a surface of asemiconductor substrate. The photoresist layer is then exposed to apattern of radiation. Typically, the chemical properties of thephotoresist regions struck by incident radiation change in a manner thatdepends on the type of photoresist used. A positive photoresist becomesoluble when exposed to the radiation, while the portion of thephotoresist that is non-exposed (or exposed less) is insoluble. Anegative photoresist becomes insoluble when exposed to the radiation,while the portion of the photoresist that is non-exposed is soluble. Adeveloper solution is then used to remove soluble portions of thephotoresist layer. Prior to application, the developer solution isfiltered using the filter 200 (FIGS. 2A and 2B, and FIGS. 4A and 4B) toremove (or otherwise minimize) metallic contaminants contained therein.

An embodiment of the present disclosure is a method 600 of developing anexposed photoresist according to the flowchart illustrated in FIG. 6. Itis understood that additional operations can be provided before, during,and after processes discussed in FIG. 6, and some of the operationsdescribed below can be replaced or eliminated, for additionalembodiments of the method. The order of the operations/processes may beinterchangeable and at least some of the operations/processes may beperformed in a different sequence. In some embodiments, at least two ormore operations/processes are performed overlapping in time, or almostsimultaneously.

The method 600 includes an operation S610 of providing a filterincluding a filter membrane and a magnet arranged about the filter. Inoperation S620, a photoresist developer including metallic contaminantsis introduced in the filter. In operation S630, metallic contaminantsare filtered from the photoresist developer using the magnet prior tothe metallic contaminants entering the filter membrane. In someembodiments, the magnet is arranged such that the magnetic field of themagnet is greater in a periphery of the filter housing compared to acentral portion of the filter housing. In some other embodiments, themagnet includes neodymium. In other embodiments, the filter includes acylindrical filter housing that encloses the filter membrane, and themagnet is a bar magnet. A plurality of the bar magnets are contactedwith the filter housing such that circumferentially adjacent bar magnetshave opposite polarity poles in contact with the filter anddiametrically opposite bar magnets have poles of a same polarity incontact with the filter housing. In still other embodiments, the magnethas an annular shape and includes poles having polarities that alternatealong a circumference of the magnet, wherein diametrically oppositepolarities of the magnet are same. In yet other embodiments, the filterincludes a cylindrical filter housing enclosing the filter membrane andthe annular shaped magnet is contacted with an outer surface of thefilter housing. In operation S640, the filtered photoresist developer isapplied to an exposed photoresist.

As discussed above, the filter 200 of FIGS. 2A-2E and FIGS. 4A-4Dfilters the metallic contaminants 251 from the solvent using magnets 204and 404, and other contaminants from the solvent using the filtermembrane 209. In some embodiments, filtering the metallic contaminantsand other contaminants is performed using separate filters. In thiscase, a first filter (e.g., a point-of use filter) is used to filtercontaminants other than metallic contaminants using the filter membrane209, for example, and a second separate filter is used to filtermetallic contaminants using magnets, as discussed above. The filters arearranged in series such that solvent exiting one filter is provided tothe other filter. Thus, in an embodiment, the first filter is arrangedbefore the second filter and thus solvent having metallic contaminantsfiltered therefrom is provided to the second filter for removing thenon-metallic or other contaminants. Alternatively, the first filter isarranged after the second filter and thus solvent having non-metallic orother contaminants filtered therefrom is provided to the first filterfor removing the metallic contaminants. By providing separate filters,the filters can be individually serviced, making the system moreefficient and economical to operate.

Referring to FIGS. 3, 5A, and 5B, it is observed that both ring-shapedmagnets and bar magnets provide improved filtering of metalliccontaminants compared to filtering in the absence of magnets. Thering-shaped magnets provide a larger contact area with the surface ofthe filter housing and increased magnetic field. Further, byincorporating the magnets (ring or bar shaped) around the filter togenerate the magnetic field according to some embodiments, changes to bemade to the filter are minimal, if needed. Thus, any structural ordesign changes made to the filter to accommodate the magnets can bequickly and economically implemented. Embodiments of the disclosurefurther improve the filtration efficiency and wafer quality, and, assuch, the wafer yield is increased. The magnetic arrangement, accordingto embodiments of the disclosure, is not limited to any particularprocess and may be used in processes using extreme ultraviolet (EUV)radiation, immersion lithography, etc.

An embodiment of the disclosure is a filter including a filter housinghaving a filter membrane for filtering solvent including metalliccontaminants, and a magnet arranged about the filter housing andconfigured to generate a magnetic field to attract the metalliccontaminants prior to the metallic contaminants entering the filtermembrane. In an embodiment, the magnet is arranged such that themagnetic field of the magnet is greater in a periphery of the filterhousing compared to a central portion of the filter housing. In anembodiment, the magnet includes neodymium. In some embodiments, themagnet is a bar magnet and the filter housing is cylindrical, aplurality of bar magnets are attached to the filter housing, andcircumferentially adjacent bar magnets have opposite polarity poles incontact with the filter housing and diametrically opposite bar magnetshave poles of a same polarity in contact with the filter housing. Inother embodiments, the magnet includes a plurality of arc segmentsarranged about the filter housing, radially inner surfaces of adjacentarc segments include opposite polarity poles, and radially innersurfaces of diametrically opposite arc segments have same polaritypoles. In some embodiments, wherein the filter housing is cylindricaland the plurality of arc segments contact an outer surface of the filterhousing. In other embodiments, wherein a plurality of magnets aredisposed about the filter. In an embodiment, the plurality of annularshaped magnets contact an outer surface of the filter housing.

Another embodiment of the disclosure is a method of developing anexposed photoresist, including providing a filter including a filtermembrane and a magnet arranged about the filter, introducing aphotoresist developer including metallic contaminants in the filter,filtering, using the magnet, metallic contaminants from the photoresistdeveloper prior to the metallic contaminants entering the filtermembrane, and applying the filtered photoresist developer to the exposedphotoresist. In an embodiment, the method further includes arranging themagnet such that a magnetic field generated by the magnet is greater ina periphery of the filter housing compared to a central portion of thefilter housing. In an embodiment, the magnet includes neodymium. In anembodiment, the filter includes a cylindrical filter housing thatencloses the filter membrane, and the magnet is a bar magnet, and themethod further includes contacting a plurality of bar magnets to thefilter housing such that circumferentially adjacent bar magnets haveopposite polarity poles in contact with the filter and diametricallyopposite bar magnets have poles of a same polarity in contact with thefilter housing. In an embodiment, the magnet includes a plurality of arcsegments arranged about the filter, adjacent arc segments have oppositepolarity poles, and diametrically opposite arc segments have samepolarity poles. In an embodiment, the filter includes a cylindricalfilter housing enclosing the filter membrane and the method furtherincludes contacting the magnet to an outer surface of the filterhousing. In an embodiment, the method further includes contacting aplurality of magnets to the outer surface of the filter housing.

Still another embodiment of the disclosure is a filter including afilter membrane for filtering solvent including metallic contaminants,and an annular magnet arranged about the filter to attract the metalliccontaminants prior to the metallic contaminants entering the filtermembrane. In an embodiment, the magnet is arranged such that a magneticfield generated by the magnet is greater in a periphery of the filtercompared to a central portion of the filter. In an embodiment, theannular magnet includes neodymium. In an embodiment, wherein the annularmagnet includes a plurality of magnetic arc segments arranged about thefilter, adjacent arc segments have opposite polarity poles, anddiametrically opposite arc segments have same polarity poles. In anembodiment, the filter includes a filter housing that encloses thefilter membrane and the annular magnet contacts an outer surface of thefilter housing. In an embodiment, a plurality of annular magnets contactan outer surface of the filter housing.

The foregoing outlines features of several embodiments or examples sothat those skilled in the art may better understand the aspects of thepresent disclosure. Those skilled in the art should appreciate that theymay readily use the present disclosure as a basis for designing ormodifying other processes and structures for carrying out the samepurposes and/or achieving the same advantages of the embodiments orexamples introduced herein. Those skilled in the art should also realizethat such equivalent constructions do not depart from the spirit andscope of the present disclosure, and that they may make various changes,substitutions, and alterations herein without departing from the spiritand scope of the present disclosure.

What is claimed is:
 1. A filter, comprising: a filter housing includinga filter membrane for filtering solvent including metallic contaminants;and a magnet arranged about the filter housing and configured togenerate a magnetic field to attract the metallic contaminants prior tothe metallic contaminants entering the filter membrane.
 2. The filter ofclaim 1, wherein the magnet is arranged such that the magnetic field ofthe magnet is greater in a periphery of the filter housing compared to acentral portion of the filter housing.
 3. The filter of claim 1, whereinthe magnet includes neodymium.
 4. The filter of claim 1, wherein themagnet is a bar magnet and the filter housing is cylindrical, aplurality of bar magnets are attached to the filter housing, andcircumferentially adjacent bar magnets have opposite polarity poles incontact with the filter housing and diametrically opposite bar magnetshave poles of a same polarity in contact with the filter housing.
 5. Thefilter of claim 1, wherein the magnet includes a plurality of arcsegments arranged about the filter housing, radially inner surfaces ofadjacent arc segments include opposite polarity poles, and radiallyinner surfaces of diametrically opposite arc segments have same polaritypoles.
 6. The filter of claim 5, wherein the filter housing iscylindrical and the plurality of arc segments contact an outer surfaceof the filter housing.
 7. The filter of claim 5, wherein a plurality ofmagnets are disposed about the filter.
 8. The filter of claim 7, whereinthe plurality of magnets contact an outer surface of the filter housing.9. A method of developing an exposed photoresist, comprising: providinga filter including a filter membrane and a magnet arranged about thefilter; introducing a photoresist developer including metalliccontaminants in the filter; filtering, using the magnet, the metalliccontaminants from the photoresist developer prior to the metalliccontaminants entering the filter membrane; and applying the filteredphotoresist developer to the exposed photoresist.
 10. The method ofclaim 9, further comprising arranging the magnet such that a magneticfield generated by the magnet is greater in a periphery of the filtercompared to a central portion of the filter.
 11. The method of claim 9,wherein the magnet includes neodymium.
 12. The method of claim 9,wherein the filter includes a cylindrical filter housing that enclosesthe filter membrane, and the magnet is a bar magnet, and the methodfurther comprises: contacting a plurality of bar magnets to the filterhousing such that circumferentially adjacent bar magnets have oppositepolarity poles in contact with the filter housing and diametricallyopposite bar magnets have poles of a same polarity in contact with thefilter housing.
 13. The method of claim 9, wherein the magnet includes aplurality of arc segments arranged about the filter, adjacent arcsegments have opposite polarity poles, and diametrically opposite arcsegments have same polarity poles.
 14. The method of claim 13, whereinthe filter includes a cylindrical filter housing enclosing the filtermembrane and the method further includes contacting the magnet to anouter surface of the filter housing.
 15. The method of claim 14, furthercomprising contacting a plurality of magnets to the outer surface of thefilter housing.
 16. A filter, comprising: a filter membrane forfiltering solvent including metallic contaminants; and an annular magnetarranged about the filter to attract the metallic contaminants prior tothe metallic contaminants entering the filter membrane, wherein theannular magnet is arranged such that a magnetic field generated by theannular magnet is greater in a periphery of the filter compared to acentral portion of the filter.
 17. The filter of claim 16, wherein theannular magnet includes neodymium.
 18. The filter of claim 16, whereinthe annular magnet includes a plurality of magnetic arc segmentsarranged about the filter, adjacent arc segments have opposite polaritypoles, and diametrically opposite arc segments have same polarity poles.19. The filter of claim 18, wherein the filter includes a filter housingthat encloses the filter membrane and the annular magnet contacts anouter surface of the filter housing,
 20. The filter of claim 19,comprising a plurality of annular magnets contacting an outer surface ofthe filter housing.